Selecting item in databound combobox before ShowDialog

Hello guys and girls,

I believe this question is kinda new-bie, but I can't solve it in correct way.

Brief description:

1. I have an inherited from ComboBox class that does some data bindings in constructor:

var mdl = new Model();

ValueMember = "id";
DisplayMember = "unit";
DataSource = mdl.getUnits();

All good here. The combobox is filled by required data.

2. Then I have another form with a function editIngridient. The function is following;

public bool editIngridient(int id)
{
currentId = id;

var row = mdl.getIngridient(id);

txtIngridient.Text = (string)row["ingridient"];
cmbUnit.ID = (int)row["unitId"];
numNotifyQty.Value = (int) row["notifyQty"];

ShowDialog();

return true;
}

3. Now, when the form popups, textbox and number box filled by needed values, while combobox is filled by first value.

4. If I will run the combobox data bind function as the first line inside editIngridient function - all works good.

Please point me to my stupidity.

Thanks a lot!